Modular phrosthesis assembly including tapered adjustments

ABSTRACT

A prosthesis assembly for implantation in a skeletal site; the assembly comprising: a first component ( 8 ) for fixation in a bone cavity ( 9 ), a second component ( 7 ) capable of direct or indirect engagement with the first component; at least one adaptor which engages the first and second components thereby allowing adjustment of the second component from a first disposition of the second component relative to a predetermined reference.

BACKGROUND

The present invention relates to improvements in surgical prostheses andmore particularly relates to a prosthesis assembly including mutuallyinteracting tapered adaptor elements capable of use in knee and otherskeletal prostheses and which allow during implantation, fineadjustability of at least one component of the prosthesis assemblythrough at least five degrees of freedom namely; rotation about X, Y andZ axes, vertical adjustment along the Z axis. Although the assembly willprimarily be described with reference to its application in adjustmentof knee prostheses and particularly tibial and femoral components, itwill be appreciated by persons skilled in the art that the double taperarrangements to be described may be applied in other prostheses atskeletal sites such as but not limited to shoulders, hips, ankles,fingers and in dental applications.

PRIOR ART

Knee arthroplasty is a well-known surgical procedure by which a diseasedand/or damaged natural knee joint is replaced by a prosthetic kneejoint. Typical knee prostheses include a tibial component, a femoralcomponent and a patellar component. Modern total knee replacementinvolves the resurfacing of the femoral condyles with a metalliccomponent, roughly approximating the shape of the anatomical femoralcondyles, and resurfacing the tibial plateau with usually, but notexclusively, a polyethylene component having a metallic tibial baseplate. Optimal conformity between the polyethylene of the tibialcomponent and the metallic femoral component has in the past been aproblem area. Ideally the femoral component should be congruent with thetop of the tibial component in order to minimise wear of a surface linerwhich is usually polyethylene. The difficulty, however, is that the kneejoint does not act as a fixed axis hinge. During normal movements of theknee, rotation of the femur upon the tibia occurs, and roll back of thefemoral condyles upon the tibia occurs, particularly when the knee isflexed. The provision of a bearing in the form of a cam mechanismbetween the femoral component and the polyethylene tibial componentmeans that with increased flexion of the knee increased posteriortranslation of the femoral component upon the tibia occurs, the bearingbetween the tibial and femoral components is incongruent and thereforetheoretically undesirable, resulting in high contact stress, leading toincreased wear of the surface liner which is usually plastics. Forexample, if the plane of the tibial plate when fitted to the tibia ismisaligned with the resected proximal surface of tie tibia, uneven wearwill result between the articular surfaces. A patient may not notice themisalignment and uneven loading of the femoral component on the tibialcomponent but where the loading is concentrated through one condyle wearis accelerated. This may lead to a reduction of up to 50% of the normallife of the prosthesis.

The femoral component generally includes a pair of spaced apart condylarportions, the superior surfaces of which articulate with a portion ofthe polyethylene tibial component. A femoral stem assembly, used toprovide lateral stability to the replaced knee joint, seats within themedullary cavity of a distal portion of a femur, and is typically fixedto the femoral component by specialized fixation, such as a collar andbolt. Some prosthetic knee joints include a taper which may be a Morsetaper, that extends from the back surface of the femoral component tomate with a femoral sleeve that is securable to the femoral stemassembly.

A femoral sleeve, which helps to fill spaces at the opening of themedullary canal, can also provide for a modular assembly allowing asurgeon to select the most appropriate femoral stem from a selection ofstems having different lengths and diameters for attachment to one of aselection of femoral components. This modular configurationsignificantly reduces the number of individual components that must bepurchased, stocked, and used during a surgical procedure. Although thefemoral stem, whatever its dimensions, is usually angled with respect tothe inferior surface of the femoral component and either off-setanteriorially/posterially or at a central location, it is sometimesdesirable to orient the femoral stem perpendicularly with respect to theback surface. For example, depending on particular patient requirements,the femoral stem may need to be offset fore or aft with respect to thefront of the femoral component. Similarly, the femoral stem may need tobe angled varying degrees to the left or right with respect to the frontplane of the femoral component. A Morse type taper post, is integrallycast as part of the femoral component. Furthermore, there is arequirement for a range of sizes of the overall femoral component.Therefore, in order to accommodate all of the possible combinations ofoverall femoral component size, fore/neutral/aft positioning of theMorse type taper post, and left/perpendicular/right angling of the Morsetype taper post, a doctor or hospital is required to maintain anundesirably substantial stock of knee prosthesis components. Despite theexistence of knee joint prostheses having modular components, thereremains a need for a modular knee joint prosthesis assembly that hasgreater versatility of adjustment to accommodate differing patientanatomy and a maligned components.

An example of a known knee prosthesis arrangement is disclosed in U.S.Pat. No. 5,593,449 to Robertson Jr. That patent discloses a dual taperstem extension for knee prosthesis for surgical implantation to apatient's leg bone at the knee joint area. The prosthesis includes aprothesis body portion that extends transversely relative to thepatients intramedullary canal for carrying a bearing surface thatarticulates with the patient's adjacent leg bone or with anotherprosthesis component. A conical connector extends from the prosthesisportion and along an ads that generally tracks the patient'sintramedullary canal. A stem member includes first and second endportions and has a central longitudinal stem axis. The stem memberincludes a socket at each end portion for forming connections to theconical connector at the respective end portions as selected by thesurgeon. One of the sockets has a central longitudinal axis thatgenerally coincides with the central longitudinal axis of the stem. Theother socket has a central longitudinal axis that forms an acute anglewith the axis of the stem. The arrangement disclosed in this patentallows the surgeon to select from a choice of two taper angles thevalgus angle for a stem extension that will best fit the patientsintramedullary canal but once the angle is selected the coupling allowsonly two degrees of freedom i.e. axial and rotational movement.

Another known knee prosthesis is disclosed in U.S. Pat. No. 5,782,921 toColleran which teaches a modular knee prosthesis including a Morse taperpost that is matable with a first portion of a femoral sleeve. A secondportion of the femoral sleeve is joined with a femoral stem that isintroducible within the medullary canal of a distal portion of a femur.The modular knee prosthesis includes a femoral component, a bolt, and aMorse taper post. The femoral component has a superior surface, aninferior surface, and an aperture. The bolt includes a head portionengagable with the superior surface of the femoral component to inhibitmovement of the bolt through the femoral component, and an elongateshaft portion that extends from the head portion of the bolt. Theelongate shaft portion has a length sufficient to protrude through theaperture beyond the inferior surface of the femoral component. The Morsetaper post is engagable with the elongate shaft portion of the bolt toretain the Morse taper post in a fixed position with respect to thefemoral component and the distal end of the Morse taper post isintroducible within a femoral sleeve.

U.S. Pat. No. 5,800,552 teaches a Mechanically linked hinged total kneeprosthesis. A resurfacing type of total knee prosthesis is disclosedwhich also provides a posterior stabilization function over the entirerange of flexion. The knee prosthesis provides primary or supplementaryposterior stabilization of the reconstructed knee joint by means of aunique mechanical cam/follower mechanism, which is integrated within themedial and lateral distal condyles of the femoral component to providefunctional compensation for lost, resected or incompetent posteriorcruciate ligaments or to work in conjunction with surgically retainedviable or questionably viable cruciate ligament structures of thereconstructed knee joint. The invention extends to prostheses includinga hinge connection that defines a posterior stabilization constructionseparate from that defined by the condyles. One embodiment of theinvention extends individually to the posterior stabilizing hingeassembly.

Another knee prosthesis disclosed in U.S. Pat. No. to McMinn comprises afemoral component, a tibial component and a meniscal componenttherebetween, a stabilising peg extending from the tibial componentthrough an elongated slot in the meniscal component and into an openingin the femoral component between a pair of condylar members thereof. Thepart of the peg extending through the slot allows the meniscal componentto rotate and also to move linearly about the peg along one path, whilstthe part of the peg in said opening engages cam surfaces on a projectionbetween said condylar members as the knee is flexed, in use, and saidlinear movement of the meniscal component occurs.

Typically a knee prosthesis will comprise a femoral component forsecuring to the femur, an opening defined by the femoral component, atibial component for securement to the tibia, an opening through thetibial component, a bearing component between the femoral and tibialcomponents, the femoral component and the bearing component havingrespective curved articulatory bearing surfaces of congruent form, anelongated slot in the bearing component, a locator separate from thetibial component, a stem part of the locator extending from an enlargedpart thereof, the stem part extending through the opening in the tibialcomponent, through the elongated slot in the bearing component, and intothe opening defined by the femoral component, the bearing componentbeing capable of rotational movement about the locator, and theelongated slot in the bearing component having a width, such as toprevent relative lateral movement between the locator and the bearingcomponent, and a length to allow linear movement of the bearingcomponent relative to the locator along one path. The linear movementoccurs, in use, upon flexion of the knee, and the enlarged part of thelocator being disposed at an opposite side of the tibial component tothat at which the bearing component engages, and being oversizedrelative to said opening through the tibial component so as to preventpassage of said enlarged part therethrough. Examples of resurfacingtypes of total knee prosthetic devices are also disclosed in thefollowing U.S. patents incorporated by reference herein. U.S. Pat. No.3,774,244 to Walker, U.S. Pat. No. 3,728,742 to Averill et al. U.S. Pat.No. 4,081,866 and U.S. Pat No. 4,207,627 to Cloutier.

Although the issue of and need for greater versatility of adjustment ofprostheses has been addressed in a number of prior art arrangements suchas those described above, there is still a need to increase theadjustability of artificial joints relative to orthogonal XY and Z axesand rotationally through multiple thee dimensional degrees of freedom tomore easily compensate for unwanted misalignments.

INVENTION

There is a long felt want in the art to provide a convenient means forfine adjustments of prostheses, where an initial fit is not inconformity with agent parameters. For example, in the case of a tibialcomponent of a knee prosthesis the tibial plate may not align with apatient reference plane. The misalignment may be in one or more planesor in one or more axes. According to present arrangements once thetibial component has been inserted as best the surgeon can, unwantedmisalignments are tolerated due to the significant problems inresetting. Accurate fixation of the tibial component to ensure properalignment is a difficult surgical objective particularly due to thedifficulty in accurately preparing the medullary cavity in the tibia. Inother bone sites and joints of the skeletal frame it would be anadvantage if a surgeon could make fine axial, rotational, lateral andanterior/posterior adjustments through multiple planes and axes as thiswould allow correction of any misalignments or non conformity withinsertion parameters.

The present invention provides an assembly including an adaptor whichallows a surgeon to make fine adjustments to a component which directlyor indirectly anchored in bone. The assembly is capable of use with avariety of bone and skeletal joint prosthesis. For instance the assemblyand associated adaptors may be applied in effecting fine adjustments todental fixations, tibial and femoral implants (distal or proximal),ankles, fingers and a variety of other joints and bone sites.

It is therefore an object of the invention to provide a modularprosthesis assembly including an adaptor which allows increasedversatility of adjustment to accommodate predetermined insertionparameters, patient anatomy, joint attitude and conditions whilemaintaining a relatively low component count. It is another object ofthe invention to provide a modular prosthesis assembly includingcomponents that are physiologically and geometrically compatible withdifferent anatomical conditions. Still another object of the inventionis to provide a modular prosthesis that is suitable for use in bonesites and joints such as but not limited to shoulders and ankles, rightand left knees. It is a farther object of the invention to provide anadaptor for use with a bone prosthesis and which allows adjustment of acomponent attached thereto through at least five degrees of freedomnamely rotation about X Y and Z orthogonal axes, axial extension alongthe Z axis and displacement relative to X and Y axes, thereby enabling asurgeon to make fine realignment adjustments to the component to moreaccurately match the component with patient geometry.

Although the invention will be primarily described with reference to itsapplication to knee prostheses it will be recognised by persons skilledin the art that the adaptor and associated taper arrangements describedherein which allow five degrees of freedom for fine adjustments to theattitude of a component may be applied in other prostheses such as maybe used to repair fingers, thumbs, shoulders and ankles. The assemblymay also be used in dental applications where a component is used toanchor an artificial tooth to a jaw bone. It will be appreciated bypersons skilled in the art that tapers other than a Morse type taper maybe used on the assembly and adaptors according to the invention.

Typically, a known modular knee prosthesis includes a femoral component,a bolt and a Morse type taper post. The femoral component bas a frontsurface, a back surface, and an aperture extending there between. Thebolt includes a head portion engagable with the front surface of thefemoral component to inhibit movement of the bolt through the femoralcomponent, and an elongate shaft portion that extends from the headportion of the bolt. The known tibial component of a knee prosthesiscomprises a tibial plate which receives a polyethylene liner whichprovides an articular surface co operating wit the femoral component.Integral with the Tibial plate is a stem adapted for insertion in amedullary cavity of tibial bone. The stem is friction fitted and may becemented into a suitably reamed medullary cavity. However if the reamedcavity is inaccurately formed, the tibial plate (or correspondingfemoral component) may sit at an angle relative to a bone section cut bythe surgeon as a reference prior to insertion of the tibial component.Once the known tibial component is inserted, the preferred way acorrecting alignment adjustment may be made is to remove the tibialcomponent and try to re set it. This is an undesirable solution tomisalignment as a refit will possibly result in a potentially weakerbone/component bond.

According to one embodiment of the invention, there is provided amodular prosthesis assembly for use in but not limited to such joints asknees and shoulders wherein the assembly includes an anchoring memberinsertable in bone, at least one adaptor and a component set accordingto a predetermined reference and which simulates anatomical geometry;wherein the adaptor engages the anchoring member and the component toallow adjustment of said component in the event the component ismisaligned with a predetermined anatomical reference.

According to another embodiment, the prosthesis assembly comprises ananchoring member insertable in a bone cavity, a tibial component whichis capable of mating with the anchoring member; an adaptor capable of cooperating with said anchoring member and the tibial component to allowfine adjustment of the tibial component.

According to a preferred embodiment, the fine adjustments of the tibialcomponent may be axial, rotational about X,Y and Z axes or offsetrelative to a longitudinal axis.

In one broad form the present invention comprises:

-   -   a prosthesis assembly for implantation in a skeletal site; the        assembly comprising;    -   a first component for fixation in a bone cavity, a second        component capable of direct or indirect engagement with the        first component;    -   at least one adaptor which engages said first and second        components thereby allowing adjustment of the second component        from a first disposition of the second component relative to a        predetermined reference.

Preferably, the first component provides an anchorage in said bone forthe assembly and receives the at least one adaptor, wherein the at leastone adaptor joins the first component to the second component.

Preferably, the joining adaptor includes a body having an externaltapered region and a tapered inner recess, wherein the external taperedregion releasably engages the first component and the inner taperedrecess receives therein the second component.

The second component is preferably adjustable through at least fourdegrees of freedom relative to said reference; namely laterally,angularly, axially or rotationally relative to X, Y and Z axes. Theexternal tapered region is preferably symmetric relative to alongitudinal axis of said adaptor.

According to one embodiment the inner taper of the adaptor is co axialwith the external taper. According to another embodiment, a longitudinalaxis of the inner taper is disposed at an angle to a longitudinal axisof said adaptor.

The inner taper may be offset relative to but parallel to a longitudinalaxis of said adaptor or the inner taper may be offset from and at anangle relative to a longitudinal axis of the adaptor. The firstcomponent includes a tapered recess which engages said external taper ofsaid adaptor and the second component preferably comprises a tibialplate connected to a tapered stem. In another embodiment the firstcomponent is a femoral implant.

In another broad form, the present invention comprises;

-   -   a modular prosthesis assembly comprising; an anchorage component        insertable in bone and a coupling component which co operates        with said anchorage component to assume a first predetermined        orientation relative to said anchorage component; the assembly        further comprising an adaptor insertable between said anchorage        component and said coupling component to allow a secondary        adjustment of said coupling component relative to said first        predetermined orientation of said coupling component.

Preferably, the anchorage member and the coupling member are capable ofengagement with each other via male/female or female/male tapers.Preferably, the adaptor is engagable with the anchorage member and thecoupling member via male/female or female/male tapers.

In another broad form the present invention comprises:

An adaptor for use with a prosthesis assembly for implantation in askeletal site, the adaptor including a body having an external taperedregion and an inner tapered recess, and wherein said external taperedregion engages a corresponding tapered recess of a first implantablecomponent of said assembly and the inner tapered recess receives thereina second component of said assembly.

The adaptor which is preferably cylindrical, allows adjustment of saidsecond component relative to a first engaged position of said secondcomponent. In one embodiment, the inner taper is co axial with the outertaper. In another embodiment, the inner taper is disposed at an angle toa longitudinal axis of said adaptor. The inner taper may be offset frombut parallel to a longitudinal axis of said adaptor. Alternatively, theinner taper is offset from and at an angle relative to a longitudinalaxis of the adaptor.

In another form the present invention comprises;

-   -   a knee prosthesis comprising a femoral component for attachment        to a femur, an opening defined by the femoral component, a        tibial component for attachment to a tibia, an opening through        the tibial component, a bearing component between the femoral        and tibial components, the femoral component and the bearing        component having respective curved articulatory bearing        surfaces; the knee prosthesis further comprising; an adaptor        capable of use with said tibial or femoral component wherein        said adaptor enables secondary orthogonal, rotational lateral        and axial adjustment of said tibial and femoral components.

In another broad form the present invention comprises:

-   -   a prosthesis assembly for implantation in a skeletal site; the        assembly comprising;    -   a first anchorage component for fixation in a bone cavity, a        second component capable of direct or indirect engagement with        the first component;    -   wherein, the anchorage component comprises a tapered recess        which receives a corresponding tapered member of said second        component, wherein said tapered recess has a longitudinal axis        which is laterally offset from and/or disposed at an angle to a        longitudinal axis of said anchorage component thereby allowing        adjustment of the second component from a first disposition of        the second component relative to a predetermined reference

In a further broad form the present invention comprises;

-   -   a modular prosthesis for implantation in a joint of a skeletal        frame, wherein the prosthesis includes a proximal component        having a part for fixation to bone and a formation for receiving        a joining member, and a distal component, wherein, the joining        member engages a distal member; said distal member including a        recess which receives therewithin at least one insertable        element, wherein said at least one element includes means to        receive and or retain said joining member; wherein said at least        one element enable orthogonal, rotational and axial adjustment        of said joining member.

In another broad form according to a method aspect the present inventioncomprises:

-   -   a method of insertion of a modular prosthesis assembly in a bone        site of a skeletal frame, wherein the modular prosthesis        assembly comprises; an anchorage component insertable in bone        and a coupling component which co operates with said anchorage        component to assume a first predetermined orientation relative        to said anchorage component; the assembly further comprising an        adaptor insertable between said anchorage component and said        coupling component to allow a secondary adjustment of said        coupling component relative to said first predetermined        orientation; the method comprising the steps of    -   a) taking an anchorage component and inserting said component in        bone;    -   b) taking a coupling component and placing said coupling        component in engagement with said anchorage component so that        the coupling component assumes a first orientation;    -   c) checking the first orientation of the coupling component to        determine if that orientation is a desired orientation relative        to a predetermined anatomical reference;    -   d) in the event that the first orientation is incorrect relative        to said anatomical reference, removing said coupling member from        engagement with said anchorage member;    -   e) engaging said adaptor with said anchorage member and engaging        said coupling member with said adaptor;    -   f) adjusting said adaptor and/or said coupling member so that        said coupling member assumes a secondary disposition which is a        preferred orientation relative to a predetermined anatomical        reference.

Preferably the adaptors include a taper, such as but not limited to aMorse which engages components having a corresponding taper.

DESCRIPTION OF DRAWINGS

The present invention will be now described according to a preferred butnon limiting embodiment and with reference to the accompanyingillustrations wherein

FIG. 1 shows an underside perspective view of a typical tibialcomponent.

FIG. 2 shows a top side view of the tibial component of FIG. 1.

FIG. 3 shows a front elevation view of the tibial component of FIG. 1.

FIG. 4 shows a side elevation view of the tibial component of FIG. 1.

FIG. 5 shows a long sectional elevation of a known tibial componentinserted in a tibial stem.

FIG. 6 shows a long sectional elevation of a known tibial componentinserted in a tibial stem having an angular offset.

FIG. 7 shows an exploded schematic view of a series of prosthesisassemblies in accordance with the present invention.

FIG. 8 shows a perspective view of an anchorage member

FIG. 9 shows a top view of the anchorage member of FIG. 8

FIG. 10 shows a long sectional view of the anchorage member of FIG. 8taken at line D-D of FIG. 11.

FIG. 11 shows an elevation view of the anchorage member of FIG. 8

FIG. 12 shows a perspective view of an anchorage member with offsetangular recess.

FIG. 13 shows a top view of the anchorage member of FIG. 12

FIG. 14 shows a long sectional view of the anchorage member of FIG. 12taken at line E-E of FIG. 15.

FIG. 15 shows an elevation view of the anchorage member of FIG. 12.

FIG. 16 shows a perspective view of a neutral revision anchorage member(tibial stem).

FIG. 17 shows a top view of the anchorage member of FIG. 16

FIG. 18 shows an elevation view of the anchorage member of FIG. 16

FIG. 19 shows a long sectional elevation view of the anchorage member of

FIG. 18 taken at G-G.

FIG. 20 shows a perspective view of a revision anchorage member (tibialstem) with lateral offset.

FIG. 21 shows a top view of the anchorage member of FIG. 20

FIG. 22 shows an elevation view of the anchorage member of FIG. 20

FIG. 23 shows a long sectional elevation view of the anchorage member ofFIG. 20 taken at F-F.

FIG. 24 shows a top view of an adaptor according to one embodiment witha laterally offset internal tapered cavity.

FIG. 25 shows a long sectional view of the adaptor of FIG. 24 taken atline A-A.

FIG. 26 shows a top view of an adaptor according to one embodiment witha laterally offset internal tapered cavity.

FIG. 27 shows a long sectional view of the adaptor of FIG. 24 taken atline B-B.

FIG. 28 shows a top view of an adaptor according to one embodiment witha laterally offset internal tapered cavity.

FIG. 29 shows a long sectional view of the adaptor of FIG. 24 taken atline C-C.

FIG. 30 shows an elevation view of a revision assembly including alateral adjustment according to one embodiment of the invention.

FIG. 31 shows a long section of the assembly of FIG. 30 taken at lineI-I.

FIG. 32 shows an elevation view of a revision assembly with verticaladjustment according to one embodiment of the invention.

FIG. 33 shows a top view of the assembly of FIG. 32.

FIG. 34 shows a long section of the assembly of FIG. 32 taken at lineH-H.

The invention will be primarily described with reference to itsapplication in knee prostheses. It will be appreciated however, that theassembly described herein including the use of an angular and/or lateraloffset for re adjustment of a component may be applied in a variety ofskeletal sites including but not limited to shoulder, ankle, finger,thumb joint. Also the assembly may be employed in dental applications.In known total knee prostheses the articular surface of the distal femurand proximal tibia are usually but not exclusively replaced withrespective metal and plastic condylar-type articular bearing components.The knee prostheses provide adequate rotational and translationalfreedom and require minimal bone resection to accommodate the componentswithin the boundaries of the available joint space. The patella-femoraljoint may also be resurfaced by a third prosthetic component, as well.

The femoral, tibial and patella prosthetic resurfacing components areaffixed to respective, surgically prepared adjacent bone structure bycementing or by biological bone ingrowth. The femoral component isusually but not exclusively a metallic alloy construction such ascobalt-chrome alloy and provides medial and lateral condylar bearingsurfaces of similar shape and geometry as the natural distal femur. Thetibial component can be made entirely of ultra high molecular weightpolyethylene or can be comprised of a metallic base and stem componentdistally and an interlocking plastic (UHMWPE) component, proximally. Theplastic tibial plateau bearing surfaces are of concave multi-radiusgeometry to more or less match the articular geometry of the matingfemoral condyles, depending upon the desired design mechanics of primaryfemoro-tibial motion, e.g. the flexion-extension, including posteriorrollback and rotational and translational articular motions.

The femoral and tibial components are positioned on the respective sideof the knee joint and are not mechanically connected or linked together(unlike the case of constrained or hinged type of knee prostheses).

Additionally, in resurfacing types of total knee prostheses the tibialplateau bearing surface geometry can assume a variety of configurations,depending upon the desired extent of articular contact and associatedtranslational (medial-lateral and anterior-posterior) and rotational(axial and varus-valgus) secondary femoro-tibial motions. These varioussecondary motions allow the resurfaced knee to function in anatural-like biomechanical manner in conjunction with the surroundingligamentous and muscle structures about the knee joint. The viable softtissue structures functionally maintain the femoral and tibial bearingsurfaces in contact, provide the necessary levels of constraining forceto achieve knee joint stability, and decelerate the principal motion inflexion-extension and secondary motions, such as axial rotation, etc. ina controlled manner. Additionally, this functional interaction been thesurrounding tissue structures and the implanted knee prosthesisminimizes abrupt motion stoppage or impact loading of properly designedprosthetic articular surfaces, and thus prevents overstressing at thecomponent fixation interface.

The objective in knee replacements is to simulate with a dynamicimplant, natural knee function as closely as possible and anyimprovement which allows a surgeon greater flexibility in achieving thisobjective is desirable. The articulation of the femoral condyles withthe tibial plateau bearing surfaces is complex biomechanics allowingprimary femoro-tibial flexion and extension, and secondary motions ofaxial and varus-valgus rotations and anterior-posterior andmedial-lateral translations, all of which occur in the normal kneejoint. The knee joint reaction forces during primary or secondary motionare principally supported by the tibial bearing surfaces, and to someextent by the cam/follower surfaces, and are transferred to theunderlying fixation interfaces and adjacent supportive bone structures.In a normal knee, physiological femoro-tibial rollback start at theonset of knee flexion and is generally mostly completed by 40 degrees offlexion. This rollback is accompanied by a transitional motion ofrolling and sliding. In the normal knee, these complex interactions areaccompanied by complex active interaction of the anterior and posteriorcruciate ligaments and other surrounding adjacent soft tissuestructures.

The above is a description of known biomechanics of a knee jointprosthesis.

The present invention described herein with reference to alternativeembodiments, provides a prosthesis assembly including adaptors whichenable a surgeon to make fine adjustments to the disposition or attitudeof a component to enable that component to be disposed such that it willallow more accurate simulation of anatomical geometry or dynamic actionat an implant site in a patient.

FIG. 1 shows an underside perspective view of a typical tibial component1. Tibial component 1 comprises a tibial plate 2 and a tibial stem 3. Anunderside surface of plate 2 may be adapted with a porous coating 4 withor without the use of a bone growth promoter Hydroxyapatite.Alternatively, as shown with reference to surface 5 the undersidesurface of plate 2 may be roughened by grit blasting. FIG. 2 shows a topside view of the tibial component 1 of FIG. 1. Plate 2 includes aformation which receives and retains a polyethylene layer which providesa bearing surface for an opposing femoral component. FIG. 3 shows afront elevation view of the tibial component 1 of FIG. 1. FIG. 4 shows aside elevation view of the tibial component of FIG. 1.

FIG. 5 shows a long sectional elevation of a known tibial component 7inserted co axially in a tibial anchorage member 8 inserted in medullarycavity 9 of tibia 10. Stem 11 of plate 14 engages recess 12 such that alongitudinal axis of stem 11 is co axial with a longitudinal axis ofrecess 12. Tibia includes a resected plateau 13 which provides areference for tibial plate 14 upon insertion in medullary cavity 9. Asshown in FIG. 5 tibial plate 14 may be out of alignment with ananatomical reference such as plateau 13. In that case, where the surgeonanticipates the possibility of an out of alignment of plate 14, ananchorage with an angular offset may be used to adjust the attitude ofplate 14. Referring to FIG. 6 there is shown a long sectional elevationof tibial component 7 inserted in a tibial stem having an angularoffset. Tibial component 7 is inserted co axially in a tibial anchoragemember 15 inserted in medullary cavity 9 of tibia 10. Stem 11 of plate14 engages recess 16 such that a longitudinal axis of stem 11 is offsetrelative to a longitudinal axis of recess 16. Tibia 10 includes aresected plateau 13 which provides a reference for tibial plate 14 uponinsertion in medullary cavity 9. As shown in FIG. 6 tibial plate 14 isnow in alignment with plateau 13 so the optimal position of tibial plate14 which is co planar with its reference plateau 13 will facilitateaccurate simulation of joint geometry.

Thus, according to one embodiment of the invention, a surgeon is able toeffect an adjustment to a component by means of an offset in providedwith or in an anchorage set in a bone site.

Referring to FIG. 7 there is shown a schematic exploded layout ofvarious components capable of use in the prosthesis assembly accordingto various embodiments. In the example of FIG. 7 there is shown a tibialcomponent 30 comprising a tibial plate 31 and stem 32. Tibial stem 32 isadapted for insertion in an anchorage member 33. Anchorage member 33comprises a body 34 including locating wings 35. Locating wings 35 allowanchorage member 33 to lock into a bone to prevent unwanted movement.Body 34 also includes a tapered recess 36 which is either co axial withor off set relative to a longitudinal axis of body 34. Anchorage member40 is similar to anchorage member 33 except that whereas in the latter,recess 36 is co anal with a longitudinal axis of body 34, in the former,a longitudinal axis of body 41 is offset relative to a longitudinal axisof recess 42. When tapered recess 36 receives and retains therein tibialstem 32, this will dictate the orientation in situ of tibial plate 31relative to anchorage member 33 and/or to a predetermined anatomicalreference. Ideally when in situ, tibial plate 31 will be parallel with abone plateau prepared by the surgeon prior to fixation of anchoragemember 33. However, as shown in FIG. 5 this is not always the case andat present the surgeon has no expedient means to make adjustments to theorientation of the tibial plate once it has been inserted (see FIG. 5).Accurate insertion of the anchorage member 33 may be inhibited by apatients bone condition or The manner of reaming of the medullary cavityprior to insertion. Errors in reaming may be translated into an error inthe disposition of tibial plate 31. In many cases the orientation oftibial plate 31 will be outside an optimum disposition for ultimatesimulation by the artificial joint of natural joint geometry andfunction. Rather than re set anchorage member 33. The present inventionallows a surgeon to make fine adjustments to improve the orientation ofthe tibial plate so it is set in a disposition required relative to apredetermined anatomical or other reference. According to oneembodiment, the surgeon may choose an off set anchorage member 40 toreceive stem 32. Offset recess 42 which also includes locating wings 43will allow the surgeon to orient the tibial plate 31 to align with apredetermined bone plateau so ultimately the completed joint willsimulate patient anatomical movement. According to an alterativeembodiment, the surgeon may choose one ore more adaptors which areinserted between tibial component 30 and either primary tibial stems 33or 40. In FIG. 7 there is shown a series of adaptors 52, 53, 54 and 55which are available for insertion between stem 32 and either anchoragemember 33 or 40. Although only four adaptors are shown it will beappreciated that a typical inventory of adaptors may be in the order of8 or more. An adaptor may be selected to allow a surgeon to adjust theorientation of tibial plate 31 in the event that when inserted in one orother of the permanently fixed anchorages 33 or 40 the orientation ofplate 31 is undesirable. Using a preselected adaptor, the surgeon mayadjust the orientation and/or attitude of tibial plate 31 rotationallyabout X, and/or Y and/or Z axes or axially along a Z axis. The adaptorsalso allow lateral displacement relative to X or Y axes. An adaptor maybe used to adjust the length of an implant, the gradient of tibial plate31 the rotation about an axis through stem 32 and to off set tibialcomponent 30 as required. Should tibial plate 31 be initially implantedwith an unwanted gradient or orientation, the surgeon now has the optionof adjusting the state of repose of tibial plate 31 so that it willinteract with condyles of a femoral implant to more accurately simulatejoint dynamics. The adaptors allow a surgeon to compensate fororientation errors in the tibial plate 31 and to eliminate the potentialfor uneven wear in the implanted prosthesis.

In another embodiment, alternative anchorage members are used to extendthe depth of penetration inside a medullary cavity. In the case of arevision where bone has degraded an allograft may be required. This willnormally necessitate a deeper anchorage in the medullary cavity. Forthis purpose revision tibial stems 44 or 45 may be used. Revision stem44 includes a male tapered end 46 capable of engagement with stemextension 47. Engagement between tapered end 46 and stem extension 47 ispreferably via a Morse taper and extends the prosthesis deep into a bonemedullary cavity to secure adequate fixation taking into account thecondition of the bone. Likewise, revision stem 45 includes a maletapered end 48 capable or engagement with stem extension 49. Engagementbetween tapered end 48 and stem extension 49 is preferably via a Morsetaper and extends the prosthesis deep into a bone medullary cavity tosecure adequate fixation taking into account the condition of the bone.Tibial stem 45 includes a lateral offset which places recess 50 out ofalignment with stem 48. The offset may be required where a directionaladjustment is required proximally.

In an alternative embodiment, in order to achieve anchorage extension adouble threaded cone 51 may be employed. Cone 51 includes recess 52which receives therein one of adaptors 52, 53, 54 and 55.

FIG. 8 shows a perspective view of an anchorage member 60 capable ofinsertion in a medullary cavity of a bone. FIG. 9 shows a top view ofanchorage member 60. Member 60 includes a tapered recess 61 and locatingwings 62 and 63 which resist unwanted rotation in a cavity in whichmember 60 is inserted.

FIG. 10 shows a long sectional view of the anchorage member 60 taken atline D-D of FIG. 11

FIG. 12 shows a perspective view of an anchorage member 64 includinglocating wings 65 and 66 and offset angular recess 67. FIG. 13 shows atop view of the anchorage member of FIG. 12 and FIG. 14 shows a longsectional view of anchorage member 64 taken at line E-E of FIG. 15.Offset recess 67 as shown in FIG. 14 is disposed at a predeterminedangle relative to longitudinal axis 68. Recess 67 receives and retainstherein a tibial component such as that shown and described in FIGS.1-4. Offset recess 67 allows the surgeon to set a tibial plate closer toa predetermined reference. elect use of an offset adjust the attitude ofa tibial plate. FIG. 16 shows a perspective view of a neutral revisionanchorage member 70 (tibial stem) according to one embodiment. Member 70is preferred for revision operations requiring allograft bone andcomprises an elongated body comprising a flared collar 71, waist 72 andtapered stem 73. FIG. 17 shows a top view of the anchorage member ofFIG. 16. Flared collar 71 includes a recess 74 which receives andretains therein stem 73. FIG. 1I shows an elevation view of theanchorage member of FIG. 16 and FIG. 19 shows a long sectional elevationview of the anchorage member 70 of FIG. 18 taken at G-G. Stem 73 locatesin recess 74. An adaptor (see FIGS. 24-29) may be secured within recess74 by means of a screw which penetrates recess 75. Anchorage member 70is characterised in that a longitudinal axis of recess 74 is co axialwith a longitudinal axis of stem 73. FIG. 20 shows a perspective view ofa revision anchorage member 80 (tibial stem) with lateral offset. Member80 is preferred for insertion in a medullary cavity in revisionoperations requiring allograft bone where deeper penetration isrequired. Anchorage member and comprises an elongated body comprising aflared collar 81, waist 82 and tapered stem 83. FIG. 21 shows a top viewof the anchorage member of FIG. 20. Flared collar 81 includes a recess84 which receives and retains therein stem 83. FIG. 22 shows anelevation view of the anchorage member of FIG. 20 and FIG. 23 shows along sectional elevation view of the anchorage member 80 of FIG. 22taken at line F-F. Stem 33 locates in recess 84. An adaptor (see FIGS.24-29) may be secured within recess 84 by means of a screw whichpenetrates recess 85. Anchorage member 80 is characterised in that alongitudinal axis of recess 84 is laterally offset relative to alongitudinal axis of stem 83. Respective recesses 74 and 84 of (tibialstem) anchorage members 70 and 80 may receive an adaptor of the typedescribed in FIGS. 24-29. These adaptors may also be used in conjunctionwith anchorage members 60 and 64 previously described.

FIG. 24 shows a top view of an adaptor 90 according to one embodimentcomprising a body 91 wilt a laterally offset internal tapered cavity 92.FIG. 25 shows a long sectional view of adaptor 90 of FIG. 24 taken atline A-A. Adaptor 90 includes a passage 93 which allows insertion of ascrew for fixation of adaptor 90 to an anchorage such as those describedin FIGS. 8, 12, 16, 20. Longitudinal axis 94 is laterally displaced frombut parallel to longitudinal axis 95 such that when adaptor 90 isinserted in an anchorage member, a coupling member (not shown) insertedin recess 92 will be laterally displaced from an otherwise neutralposition. A fine lateral adjustment may be an advantage for an implantwhich is not initially disposed in an optimal alignment.

FIG. 26 shows a top view of an adaptor 96 according to one embodimentwith a laterally offset internal tapered cavity. FIG. 27 shows a longsectional view of the adaptor of FIG. 26 taken at line B-B. Adaptor 96includes a passage 99 which allows insertion of a screw for fixation ofadaptor 96 to an anchorage such as those described in FIGS. 8, 12, 16,20. Longitudinal axis 100 is at an angle to longitudinal axis 101 suchthat when adaptor 96 is inserted in an anchorage member, a couplingmember (not shown) inserted in recess 98 will be disposed at an anglefrom an otherwise neutral position. A fine lateral adjustment may be anadvantage for an implant which is not initially disposed in an optimalalignment. FIG. 28 shows a top view of an adaptor 102 according to oneembodiment with a body 103 having internal tapered cavity 104. Cavity104 is in axial alignment with a longitudinal axis 105 of adaptor 102,FIG. 29 shows a long sectional view of the adaptor 102 of FIG. 24 takenat line C-C.

FIGS. 30-34 show examples of adjustments which may be made using arevision prosthesis assembly. Shown by way of example are lateral,horizontal angular and vertical angular adjustments which a surgeon maymake in a revision assembly. FIG. 30 shows an elevation view of arevision assembly 110 according to one embodiment of the invention.Assembly 110 comprises a tibial component 111 comprising a tibial plate112 and a tibial stem 113. Tibial stem 113 locates in internal taperedrecess 114 of adaptor 115. Adaptor 115 accommodates stem 113 via meansof interfitting tapers. The assembly 110, includes tibial revision stem116 which engages via tapered end 117 an extension member 118. FIG. 31shows a long section of the assembly of FIG. 30 taken at line I-L. Asmay be seen from FIG. 31 a longitudinal axis 119 of adaptor 115 islaterally offset from longitudinal axis 120 of extension tibial visionstem (anchorage) 116 and extension 118. As shown in FIG. 31, laterallyoffset recess 121 may be combined with another offset cavity in adaptor115 so that within that assembly there is a range of adjustment. Thusthere may typically be anywhere between 1-6 mm of lateral adjustmentdepending upon how adaptor 15 is located in offset tapered recess 121.This range may vary (decrease or increase) according to the size of thecomponents.

FIG. 32 shows an elevation view of a revision assembly similar to thatshown in FIG. 31, according to one embodiment of the invention. FIG. 33shows a top view of the assembly of FIG. 32 indicating relative to axes122 and 123 available horizontal angular adjustment of tibial plate 112.FIG. 34 shows a long section of the assembly of FIG. 32 taken at lineH-H. Reference axes 124 and 125 indicate available angular adjustmentenabled by angular offset adaptor 115. The revision assembly may beadjusted by selection of adaptors such as those shown in FIGS. 24-29.Tapers enabling fitting of adaptors to an anchorage member arepreferably Morse tapers. The arrangements described above with referenceto a tibial component are adaptable also to a corresponding femoralcomponent of a knee prosthesis.

Typically a femoral component includes a proximal shaft member forinsertion in a medullary cavity of a femur. According to one embodiment,the shaft may be a known double threaded cone (Margron ™) forcompressive fixation. The proximal shaft includes a tapered recess whichreceives a joining element. The femoral component further comprises adistal element having a recess which receives and retains an adaptorhereinbefore described. This effectively provides a taper within a taperand allows the ability to fit a fixture on the taper thereby allowingadjustment by rotation, offset, vertical height and horizontaladjustment in three dimensions (i.e. relative to XY&Z axes.

For any joint prosthesis replacement including the knee to functionoptimally 4 vectors need to be considered in the design to return thejoint position in space to as normal as possible a natural position. Thefour vectors are;

-   -   1 medial-lateral    -   2 anterior-posterior    -   3 rotational    -   4 vertical height

The four axis double taper arrangement allows for correction in all 4degrees of freedom to accomplish that objective. The jointingarrangement described above using an offset taper within a taper willassist a surgeon in finding appropriate joint references accurately suchas the horizontal line.

The inserts described herein may be manufactured from Chrome cobalt orTitanium.

It will be recognised by persons skilled in the art that numerousvariations and modifications may be made to the invention broadlydescribed herein without departing from the overall spirit and scope ofthe invention.

1. A prosthesis assembly for implantation in a skeletal site: theassembly comprising; a first component for fixation, in. a bone cavity,a second component capable of direct or indirect engagement with thefirst component; at least one adaptor which engages said first andsecond components thereby allowing adjustment of the second componentfrom a first disposition of the second component relative to apredetermined reference.
 2. A prosthesis assembly according to claim 1wherein the first component provides an anchorage in said bone for theassembly and receives said at least one adaptor.
 3. A prosthesisassembly according to claim 2 wherein the at least one adaptor joins thefirst component to the second component.
 4. A prosthesis assemblyaccording to claim 3 wherein said joining adaptor includes a body havingan external tapered region and a tapered inner recess.
 5. A prosthesisassembly according to claim 4 wherein said external tapered regionreleasably engages said first component
 6. A prosthesis assemblyaccording to claim 5 wherein, said inner tapered recess receives thereinsaid second component.
 7. A prosthesis assembly according to claim 6wherein, the second component is adjustable through at least fourdegrees of freedom relative to said reference.
 8. A prosthesis accordingto claim 7 wherein each said at least one adaptor allows adjustment ofsecond component laterally, angularly, axially or rotationally relativeto x, y and z axes.
 9. A prosthesis assembly according to claim 8wherein the external tapered region is symmetric relative to alongitudinal axis of said adaptor
 10. A prosthesis assembly according toclaim 9 wherein the inner taper of the adaptor is co axial with theexternal taper.
 11. A prosthesis assembly according to claim 9 wherein alongitudinal axis of the inner taper is disposed at an angle to alongitudinal axis of said adaptor.
 12. A prosthesis assembly accordingto claim 9 wherein, said inner taper is offset relative to but parallelto a longitudinal axis of said adaptor.
 13. A prosthesis assemblyaccording to claim 9 wherein said inner taper is offset from and at anangle relative to a longitudinal axis of the adaptor.
 14. A prosthesisassembly according to claim 1 wherein said first component, includes atapered recess which engages said external taper of said adaptor.
 15. Aprosthesis assembly according to claim 14 wherein said second componentcomprises a tibial plate connected to a tapered stem.
 16. A prosthesisassembly according to claim 14 wherein the first component is a femoralimplant.
 17. A prosthesis according to claim 15 wherein said adaptorallows adjustment of an angle of repose of said tibial plate.
 18. Amodular prosthesis assembly comprising; an anchorage componentinsertable in bone and a coupling component which cooperates with saidanchorage component to assume a first predetermined orientation relativeto said anchorage component; the assembly further comprising an adaptorinsertable between said anchorage component and said coupling componentto allow a secondary adjustment of said coupling component relative tosaid first predetermined orientation of said coupling component.
 19. Anassembly according to claim 18 wherein the anchorage member and thecoupling member are capable of engagement with each other viamale/female or female/male tapers.
 20. An assembly according to claim 19wherein said adaptor is engageable with said anchorage member and saidcoupling member via male/female or female/male tapers.
 21. An adaptorfor use with a prosthesis assembly for implantation in a skeletal site,the adaptor including a body having an external tapered region and aninner tapered recess, and wherein said external, tapered region engagesa corresponding tapered recess of a first implantable component of saidassembly and the inner tapered recess receives therein a secondcomponent of said assembly.
 22. An adaptor according to claim 11 whereinthe adaptor allows adjustment of said second component relative to afirst engaged position of said second component.
 23. An adaptoraccording to claim 22 wherein the adaptor is cylindrical.
 24. An adaptoraccording to claim 23 wherein the inner taper is co axial with the outertaper.
 25. An adaptor according to claim 24 wherein a longitudinal axisof the inner taper is disposed at an angle to a longitudinal axis ofsaid adaptor.
 26. An adaptor according to claim 25 wherein said innertaper is offset from but parallel to a longitudinal axis of saidadaptor.
 27. An adaptor according to claim 26 wherein said taper isoffset from and at an angle relative to a longitudinal axis of theadaptor.
 28. An adaptor according to claim 27 wherein said firstcomponent provides and anchorage for said second component
 29. A kneeprosthesis comprising a femoral component for attachment to a femur, anopening defined by the femoral component, a tibial component forattachment to a tibia, an opening through the tibial component, abearing component between the femoral and tibial components, the femoralcomponent and the bearing component having respective curvedarticulatory bearing surfaces; the knee prosthesis further comprising anadaptor capable of use with said tibial of femoral component; whereinsaid adaptor enables secondary orthogonal, rotational lateral and axialadjustment of said tibial and femoral components.
 30. A prosthesisassembly for implantation in a skeletal site; the assembly comprising; afirst anchorage component for fixation in a bone cavity, a secondcomponent capable of direct or indirect engagement the first component;wherein, the anchorage component comprises a tapered recess whichreceives a corresponding tapered member of said second component;wherein said tapered recess has a longitudinal axis which is laterallyoffset from and/or disposed at an angle to a longitudinal axis of saidanchorage component thereby allowing adjustment of the second componentfrom a first disposition of the second component relative to apredetermined reference.
 31. A method of insertion of a modularprosthesis assembly in a bone site of a skeletal frame, wherein themodular prosthesis assembly comprises; an anchorage component insertablein bone and a coupling component which co operates with said anchoragecomponent to assume a first predetermined orientation relative to saidanchorage component; the assembly further comprising an adaptorinsertable between said anchorage component and said coupling componentto allow a secondary adjustment of said coupling component relative tosaid first predetermined orientation; the method comprising the steps ofa) taking an anchorage component and inserting said component in bone;b) taking a coupling component and placing said coupling component inengagement with said anchorage component so that the coupling componentassumes a first orientation; c) checking the first orientation of thecoupling component to determine if that orientation is a desiredorientation relative to a predetermined anatomical reference; d) in theevent that the first orientation is incorrect relative to saidanatomical reference, removing said coupling member from engagement withsaid anchorage member; e) engaging said adaptor with said anchoragemember and engaging said coupling member with said adaptor; adjustingsaid adaptor and/or said coupling member so that said coupling memberassumes a secondary disposition which is a preferred orientationrelative to a predetermined anatomical reference.